验证码制作之五: 绘制带背景图的图形验证码方法

using System;

using System.Data;

using System.Configuration;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.Drawing;

using System.Drawing.Imaging;

using System.Drawing.Drawing2D;
public partial class _Default : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

if (!IsPostBack)

{

string checkCode = CreateRandomCode(4);

CreateImage(checkCode);

}

}

//产生随机代码

private string CreateRandomCode(int codeCount)

{

string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z";

string[] allCharArray = allChar.Split(',');

string randomCode = "";

int temp = -1;

Random rand = new Random();

for (int i = 0; i < codeCount; i++)

{

if (temp != -1)

{

rand = new Random(i * temp * ((int)DateTime.Now.Ticks));

}

int t = rand.Next(35);

if (temp == t)

{

return CreateRandomCode(codeCount);

}

temp = t;

randomCode += allCharArray[t];

}

return randomCode;

}

private void CreateImage(string checkCode)

{

if (checkCode == null || checkCode.Trim() == String.Empty)

return;

Bitmap image = new Bitmap(checkCode.Length * 12 + 10, 22);

Graphics g = Graphics.FromImage(image);

try

{

//生成随机生成器

Random random = new Random();

//清空图片背景色

g.Clear(Color.White);

//画图片的背景噪音线

for (int i = 0; i < 25; i++)

{

int x1 = random.Next(image.Width);

int x2 = random.Next(image.Width);

int y1 = random.Next(image.Height);

int y2 = random.Next(image.Height);

g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);

}

Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));

LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.BlueViolet, Color.Crimson, 1.2f, true);

g.DrawString(checkCode, font, brush, 2, 2);

//画图片的前景噪音点

for (int i = 0; i < 100; i++)

{

int x = random.Next(image.Width);

int y = random.Next(image.Height);

image.SetPixel(x, y, Color.FromArgb(random.Next()));

}

//画图片的边框线

g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

System.IO.MemoryStream ms = new System.IO.MemoryStream();

image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

Response.ClearContent();

Response.ContentType = "image/Gif";

Response.BinaryWrite(ms.ToArray());

}

finally

{

g.Dispose();

image.Dispose();

}

}

}